Add missing acorn dependency for node@12 and node@14

Author: deleonn

package-lock.json

@@ -46,6 +46,7 @@
   ],
   "license": "Apache-2.0",
   "devDependencies": {
+    "acorn": "^8.7.1",
     "babel-cli": "^6.9.0",
     "babel-eslint": "^6.0.4",
     "babel-plugin-add-module-exports": "^0.1.2",